The present invention relates to a method and apparatus for the continuous automatic manufacture of a plurality of plastic bags or pouches from a continuous web of thermoplastic film, such as polyethylene, polypropylene, etc. Such plastic bags are used for a variety of purposes, including the display-packaging of small articles of clothing, small parts for the automative and electronic fields, etc.
Bags of this general type are now formed to some degree of completion on conventional elongate side-weld bag-making machines and pouch bag-making machines commercially available under the trade names Shejldal by Webster Industries, Poly Star by Rowan Industries, FMC and other companies. Such machines are either split tandem machines which process two webs of film, side-by-side, to simultaneously form bags along each side of the machine, or single web machines which process a single web of film.
Reference is made to U.S. Pat. Nos. 3,670,947, 3,782,622 and 4,590,610 for their disclosure of plastic bags incorporating closure flaps and hangers, and to U.S. Pat. No. 4,385,722 for its disclosure of such bags and an apparatus for manufacturing the same from a continuous web of thermoplastic film, although the hangers thereof must be inserted manually and secured by means of adhesive.
In most commercially-available plastic bags of the present type, incorporating hangers, the hangers are heat-fused to the bags either within the flap or external thereto. This requires that the film and the hangers consist of the same thermoplastic composition so that they fuse together at the same temperature. However, in many cases it is desirable to produce bags from different plastic films without being concerned about the composition of the hangers.
The known conventional continuous bag-making machines are unsatisfactory for the automatic production of bags of the type disclosed in U.S. Pat. No. 4,590,610, having hangers loosely confined within an upper flap portion, due to the absence of any known means for automatically inserting the hangers thereof, and due to the difficulty of maintaining even manually-inserted hangers in centered position relative to each bag-width because the tension applied to cause movement of the continuous web causes the web to creep or stretch out of alignment so that the hangers become off-center. When alignment or longitudinal integrity is lost, the physical features applied at the workstations become off-center relative to the final transverse cuts, to form disfigured and unsatisfactory bags. This requires that the machine be shut down and readjusted. For each minute of down time a tandem machine is not making bags at the normal rate of 120 to 140 per minute, 60 to 70 per side. Most importantly, the machine operator must manually readjust the positions of each of the workstations, relatively to each other and to the final cutting station, so that the hangers are attached in centered position, the flaps are properly cut, the adhesive tabs are centered, etc. This is time consuming and requires multiple trial and error adjustments before all bag features are perfectly centered and aligned.